1. Field of the Invention
The present invention relates to a preamplifier, and in particular to improvement of a vacuum tube preamplifier of differential amplification type.
2. Description of Prior Art
In a differential amplification type vacuum tube preamplifier for audio application, two vacuum tubes are combined together to achieve differential amplification. Positive voltage is applied to plates of the two vacuum tubes via plate resistor, and output signal is picked up from the plate of one of the vacuum tubes. FIG. 5 shows an arrangement of a conventional vacuum tube differential preamplifier as described above.
In a conventional differential preamplifier as described above, problem arises in that noise components are intermingled via power line and quality of output signal is deteriorated. Specifically, in a preamplifier to amplify audio signal, the influence of distortion or noise must be reduced as much as possible because intermingling of noise from power source causes serious problem and quality of audio signal is deteriorated.